Mystery Wave in Milky Way Galaxy Suggests Recent Crash

Large cacti appear to point at the sky in the Chilean Atacama Desert. The Milky Way dominates the image, with the Large Magellanic Cloud in the lower right. These cacti (Echinopsis atacamensis) grow on average 0.4 inches (1 centimeter) per year, and reach heights of up to 30 feet (9 meters). These particular plants are found on the winding road connecting ESO's Atacama Large Millimeter/submillimeter Array (ALMA) Operation Support Facility to the Array Operation Site at ESO, at an altitude of about 11,500 feet (3500 meters) CREDIT: ESO/S. Guisard View full size image

"We have found evidence that our Milky Way had an encounter with a small galaxy or massive dark matter structure perhaps as recently as 100 million years ago," said Larry Widrow, a professor at Queen’s University in Canada. "We clearly observe unexpected differences in the Milky Way’s stellar distribution above and below the Galaxy's midplane that have the appearance of a vertical wave — something that nobody has seen before."

An illustration of our Milky Way galaxy noting its mass distribution. Scientists suspect a recent collision with a dwarf galaxy possibly as recent as 100 million years ago, created a mysterious wave in our galaxy. Image posted July 9, 2012.
CREDIT: Fermilab

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About 60 miniature "dwarf galaxies" have been discovered orbiting the Milky Way. Theory suggests that many invisible dark matter satellites also circle our galaxy, though these would only be detectable by their gravitational pull.

It's likely that one of these may have slammed into the Milky Way, though even that is not certain.

"The perturbation need not have been a single isolated event in the past, and it may even be ongoing," said Susan Gardner of the University of Kentucky. "Additional observations may well clarify its origin."

The research is detailed in a recent edition of the Astrophysical Journal Letters.

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